Hey! I noticed your friend request. Sorry that I haven't accepted or rejected it yet; I go through periods of inactivity and often come back no longer remembering where I may have spoken with people in the past, and I prefer to keep my friend's list narrowed down to people whose distinct personalities I can remember.
If you would like to talk back and forth for a bit so I can get to know you first, that'd be great! If you can actually remember where, it'd help if you could let me know what we were talking about when you decided that you wanted to add me; then I might remember the conversation and thus remember you.
I know I've just now written this message to multiple people, but I hope you can still see this as genuine.